More runners than ever before—from elites to midpackers—are talking about running technique and debating its importance. Which begs the question: Should you change your form? That depends...

Yet Higgins is one of the better runners in the United States. Her fastest marathon, 2:33:06, placed her seventh at the 2008 Chicago Marathon and made her the eighth-quickest woman in the country that year. She has a shoe contract with Saucony, runs up to 140 miles per week, and has won a national title at 25-K. In 2009, she represented the United States in the marathon at the World Championships in Berlin.

Still, while Higgins is accomplished, her career has been up and down. Pro runners live precarious lives. Most get one or two shots at a big payday or Olympic berth; if they fall short, it becomes hard to stay in the sport. By early 2010, two years after quitting her job as an art teacher, moving from Colorado to Arizona, and joining a full-time training group, Higgins hadn't cracked the elite tier of American marathoners. With her coach, Greg McMillan, she was engaged in an increasingly desperate search for a breakthrough performance, and after a series of so-so marathons, she and McMillan decided that her form was partially to blame. So they decided to rebuild it from the ground up.

McMillan coaches 19 postcollegiate athletes, and only Higgins has undergone a form overhaul. By the time runners reach his group, they often have as many as 10 years of competitive running behind them, and like any repetitive activity, the mechanics of running eventually harden and don't easily change. McMillan sometimes cleans up his runners' form, adjusting an arm angle or encouraging better knee lift, but he has avoided altering the essential nature of a runner's stride.

Higgins's form, however, needed a good deal of attention. Though she ran upright, she was heel-striking and her stride rate was too high—even at an easy pace, she took more than 200 steps per minute, and McMillan believed that she would be better taking 180, which is widely considered ideal. McMillan thought that years of high-mileage training had turned Higgins into a runner who was efficient but lacked power—she could run forever, but her racing ability at short distances was relatively poor considering her marathon time. "We were running into a speed limitation, not an endurance limitation," McMillan said.

The scientific community believes that runners who heel-strike may waste energy. Runners who land on their midfoot don't brake their body weight as they hit the ground, conserving energy and slowing the rate at which impact forces travel up the leg. "If you treat the leg like a spring, it catches the body and pops it back up in the air," says Peter Weyand, Ph.D., a professor of applied physiology and biomechanics at Southern Methodist University. In a midfoot strike, Weyand says, the muscle and tendon structure absorbs, stores, and releases energy without much waste. (For a sense of how that feels, try taking a few strides on your midfoot. You should feel your quads and calves working harder, which means that they—not your bones—are absorbing energy.) But when researchers graph the energy-return patterns of heel-strikers, they see something else. "The heel-strike is dissipated energy," Weyand says. In severe heel-strikers, impact forces are absorbed by the bone structure, which does not store energy well. Theoretically, the harder the heel-strike, the more energy is lost. Current technology is not sophisticated enough to capture what that might mean in a race, but Weyand believes it is modest, though not insignificant. "Two or three percent for these elites is huge," he says. For Higgins, three percent might mean almost a five-minute improvement—the difference between making the Olympics and going back to teaching art.